Acidic

This item has a slick-looking, greenish sheen, and a light, acrid-smelling mist constantly rises from its surface.

A thin film of acid continuously covers the surface of this armor or shield, which is not damaged by this effect. An acidic suit of armor or shield deals 2d4 points of acid damage per full round of contact to each opponent grappling you, and to any object that remains in direct contact with it (except objects you are holding) for that amount of time. However, the acid deals no damage to creatures or objects that remain in contact with it for less than a full round, such as when a creature makes a melee attack against you.